A fissure should not turn into a fistula. A fistula is a tunnel from one organ to another or to the outside of the body. I have not heard of a fistula starting on the outside of the body and going to an organ.

Fissures are tears in the lining of the anus. I don't believe they can turn into anything. They can run deep and often expose the muscle underneath (one of mine is). A fistula is a tunnel between 2 parts or organs. I have one that is skin to rectum which was caused by an abcess. An abcess is a pocket of infection sort of like a bubble. The fissures can't turn into that bubble. If you get an infection due to the fissures you might form an abcess nearby but the actual fissure can't turn into anything. Hope it helps!Descrapster